A camera is often used with a position measurement system, such as a global navigation satellite system (GNSS) or an inertial navigation system (INS), to associate position and image information. Position and image information can be used, for example, with known photogrammetry techniques to determine the three-dimensional coordinates of points on objects. Such techniques may include measurements made in two or more overlapping photographic images taken from different positions. The photogrammetric measurements are made with respect to a perspective center of the camera, and the position measurements are made with respect to a center of the position measurement system (e.g., a phase center of an antenna or an axis of rotation of an INS unit). The photogrammetric measurements are typically defined relative to a camera coordinate frame, while the position measurements are typically defined relative to a real world or local coordinate frame.
The center of the position measurement system can be defined in the camera coordinate frame by fixing the camera to the position measurement system and calibrating the integrated device. This fixes the offset between the center of the position measurement system and the perspective center of the camera. Even with the camera fixed to the position measurement system, however, it is difficult to define the perspective center of the camera in the real world coordinate frame. The translation in x, y, and z directions must be accounted for, as well as the rotation about the x, y, and z axes. The computations require at least a knowledge of the rotation of the system about the x, y, and z axes, an over-constrained system of photogrammetric and position measurements, and/or points in the images with known coordinates in the real world coordinate frame. Obtaining this data generally requires additional hardware, increases computational complexity, and/or increases noise leading to inaccurate and unreliable results.
Thus, there is a general need in the art for improved systems for associating position and image information.